This invention pertains to oscillators and more particularly to phase-locked loop oscillators.
Phase-locked loop oscillators have many applications wherein a local oscillator must be synchronized to received signals. A common use is in the horizontal and vertical circuits of a television receiver. Another use is in the recovery of data.
In particular the recovery of data from computer peripheral equipment, such as a magnetic tape or disc, is generally implemented with a phase-locked loop system. Such a system provides for the separation of data and clocking information in an intermixed format.
Present day data formats such as modified frequency modulation, modified modified frequency modulation and group coded recording present additional requirements on the phase-locked loop system. Since these formats can omit one or more transitions, the time constant of the phase-locked loop must be sufficiently long so as not to be affected by these omitted transitions. In a situation where rapid successive read commands are issued by the controlling device, phase-lock loop recovery may not be possible in the time required.